This invention relates to a new aluminosilicate zeolite comprising a MTT framework designated UZM-53 and its use as a catalyst in hydrocarbon conversion processes. This zeolite is represented by the empirical formula:M+mRrAl1-xExSiyOz M+mRrAl1-xExSiyOz where M represents sodium, potassium or a combination of sodium and potassium cations, R is the organic structure directing agent or agents derived from reactants R1 and R2 where R1 is diisopropanolamine and R2 is a chelating diamine, and E is an element selected from the group consisting of gallium, iron, boron and mixtures thereof. UZM-53 has utility in various hydrocarbon conversion reactions such as oligomerization.
Zeolites are crystalline aluminosilicate compositions which are microporous and which are formed from corner sharing AlO2 and SiO2 tetrahedra. Numerous zeolites, both naturally occurring and synthetically prepared, are used in various industrial processes. Synthetic zeolites are prepared via hydrothermal synthesis employing suitable sources of Si, Al and structure directing agents such as alkali metals, alkaline earth metals, amines, or organoammonium cations. The structure directing agents reside in the pores of the zeolite and are largely responsible for the particular structure that is ultimately formed. These species balance the framework charge associated with aluminum and can also serve as space fillers. Zeolites are characterized by having pore openings of uniform dimensions, having a significant ion exchange capacity, and being capable of reversibly desorbing an adsorbed phase which is dispersed throughout the internal voids of the crystal without significantly displacing any atoms which make up the permanent zeolite crystal structure. Zeolites can be used as catalysts for hydrocarbon conversion reactions, which can take place on outside surfaces as well as on internal surfaces within the pore.
As used herein, zeolites may be referred to by proper name, such as ZSM-23, or by structure type code, such as MTT. These three letter codes indicate atomic connectivity and hence pore size, shape and connectivity for the various known zeolites. The list of these codes may be found in the Atlas of Zeolite Framework Types, which is maintained by the International Zeolite Association Structure Commission at http://www.iza-structure.org/databases/. The structure type MTT has been described in the literature and is known to contain 1-dimensional 10-ring channels normal to the c axis. Zeolites are distinguished from each other on the basis of their composition, crystal structure and adsorption properties. One method commonly used in the art to distinguish zeolites is x-ray diffraction.
Several related molecular sieves have been disclosed but there are significant differences between those molecular sieves and those of the present invention. Plank, Rosinski, and Rubin describe ZSM-23, the MTT type material, in U.S. Pat. No. 4,076,842 as having a SiO2/Al2O3 ratio of from 40-250 and preferably from 50-220. ZSM-23 is synthesized using a nitrogen-containing organic cation. Valyocsik, describing an improved method of synthesis of ZSM-23 in U.S. Pat. No. 4,490,342 describes ZSM-23 as having a SiO2/Al2O3 ratio of from 40-5000 and preferably from 50-2000. ZSM-23 is synthesized using an organic cation of the formula (CH3)3N+—R1-+N(CH3)3. The present invention involves a SiO2/Al2O3 ratio of less than 60, preferably less than 50 and most preferably less than 44 and is not synthesized using an organic nitrogen-containing cation. Attempts to synthesize ZSM-23 at a SiO2/Al2O3 ratio of less than 50 led to the formation of ZSM-35, a material of FER structure type as disclosed in U.S. Pat. No. 4,016,245.
U.S. Pat. No. 4,837,000 discloses a crystalline silicate, ISI-4, with a specific XRD pattern that is synthesized in the presence of relatively large amounts of ethylene glycol or monoethanolamine.
Parker and Bibby describe the synthesis of KZ-1 in ZEOLITES 1983, 3, 8-11 from reactant compositions comprising pyrrolidine, dimethylamine or 2-aminopropane ranging from a SiO2/Al2O3 ratio of from 55-110 to give a product with a particular XRD pattern and typically having a BET surface area of about 160 m2/g. The present invention is made at lower Si/Al2 ratios than KZ-1.
Di Renzo and coworkers describe in U.S. Pat. No. 5,314,674 the synthesis of a MTT zeolite with a particular XRD pattern in the absence of any nitrogenous organic agent and in the presence of ethanol. The UZM-53 of the instant invention is synthesized in the presence of two nitrogenous organic agents and in the absence of ethanol.
Zones describes SSZ-32 in U.S. Pat. No. 5,053,373 in the as-synthesized and anhydrous state as having a characteristic XRD pattern, a SiO2/Al2O3 ratio of from 20 to less than 40 and comprising an N-lower alkyl-N′-isopropyl-imidazolium cation such as N,N′-diisopropylimidazolium cation. As prepared, the SiO2/Al2O3 ratio is typically from 25:1 to about 37:1 and can be increased by treating the zeolite with chelating agents or acids to extract aluminum from the zeolite lattice.
Zones and coworkers describe in U.S. Pat. No. 7,390,763 the preparation of SSZ-32X, a MTT zeolite of a certain XRD pattern and a SiO2/Al2O3 ratio of from 20 to less than 40 and preferably from 30 to 35 and comprising, in the as-synthesized and anhydrous form, an N-lower alkyl-N′-isopropyl-imidazolium cation such as N,N′-diisopropylimidazolium cation and an alkylamine such as isobutylamine.
Burton and Zones describe a process for preparing MTT zeolites and MTT zeolite compositions in U.S. Pat. No. 7,157,075 where the MTT zeolites synthesized have a composition in the as-synthesized and anhydrous state with a SiO2/Al2O3 ratio of greater than 15, a ratio of at least one nitrogen-containing organic compound selected from a group including N,N,N′,N′-tetramethylpropanediamine to SiO2 of from 0.02 to 0.10 and a ratio of alkali metal cation (or alkaline earth cation or mixtures thereof) to SiO2 of from 0.015 to 0.1.
Nakagawa discloses in U.S. Pat. No. 5,707,601 processes for synthesizing MTT zeolites such as SSZ-32 utilizing small amines such as isobutylamine as the organic structure directing agent. These MTT zeolites have specific XRD patterns and compositions different from those of the instant invention.
Rouleau and coworkers describe in U.S. Pat. No. 6,475,464 an MTT zeolite and process for preparing said zeolite wherein the synthesis is carried out using at least one alkylated polymethylene α-ω diammonium derivative and seeds of a zeolitic material different from the MTT zeolite to be prepared. The present invention does not utilize a diammonium compound, nor are seeds of a framework other than MTT used to crystallize the instant zeolite.
Barri describes in GB2190910 the synthesis of a product they call ZSM-23 from the crystallization of a gel comprising diisopropanolamine and having a SiO2/Al2O3 ratio of greater than 50 and preferably in the range from 60 to 500. The present invention involves a SiO2/Al2O3 ratio of less than 60, preferably less than 50 and most preferably less than 44.